Phencyclidine HC1 (PCP) will be established as a reinforcer orally for eight rhesus monkeys according to reliable procedures previously developed in this laboratory to produce ethanol-etonitazene- and pentobarbital-reinforced behavior. These oral procedures will serve as a basis for the development of new research strategies that may later be used with PCP analogs and other drugs. The behavioral experiments to be described are based on principles of operant conditioning. The proposed research will provide information concerning: 1) variables that control PCP-reinforced behavior; 2) factors affecting tolerance to PCP; 3) interactions of PCP with other drugs; and 4) the effects of chronic PCP access and its termination. Once PCP is established as a reinforcer, the maintenance of this behavior will be investigated with a range of PCP concentrations, using a fixed ratio (FR), a fixed interval (FI) and a multiple FI FR schedule. Food availability (deprivation and satiation) is an additional independent variable that has recently been reported by this laboratory to have a powerful effect etonitazene- (Via oral and intravenous routes) and cocaine-(intravenous) reinforced behavior. The effects of food deprivation and food satiation on PCP-reinforced behavior will be determined. The development, loss, and reacquisition of tolerance to PCP will be examined under conditions whereby the monkeys are self-administering PCP and the drug is serving as a reinforcer. Subsequently, daily versus intermittent (every 2, 4, or 8 days) access to PCP will be compared with respect to tolerance. In another experiment the interaction of PCP with d-amphetamine and pentobarbital will be investigated under two conditions: 1) PCP will be self-administered and the second drug will be injected parenterally and 2) each drug will be combined with PCP and will then be orally self-administered. Finally, the effects of chronic access to PCP will be recorded in terms of gross measures such as food and water intake, activity and body weight as well as performance on a complex behavioral schedule. These measures will also be made after abrupt termination of PCP accesss.